As described in Japanese Patent Publications No. 46(1971)-15326 and No. 49(1974)-441, there is known a method comprising imagewise exposing a photosensitive transfer material consisting essentially of a support, a peel layer made of an organic polymer and an image-forming layer (color material-containing photosensitive layer or a composite layer of a color material layer and a photosensitive layer), superposed in this order, then developing the photosensitive transfer material to form a color image on the peel layer, and transferring the color image onto an optional support (permanent support) using an adhesive. This method has such a merit that various operations such as an overlay type operation and a surprint type operation can be utilized as a color proofing operation for the method. However, this method also has a demerit that the process of the method is complicated because an adhesive is necessarily used in each transferring stage and it is difficult to keep the accuracy in the adjustment of each image position during the transferring stage.
For improving the complicated process, a method of transferring the obtained image onto the permanent support under application of heat and pressure is disclosed in Japanese Patent Provisional Publications No. 47(1972)-41830, No. 48(1973)-9373 and No. 51(1976)-5101. Particularly, Japanese Patent Provisional Publication No. 51(1976)-5101 describes that a heat-fusible polymer layer is provided as an adhesive layer on the permanent support, and Japanese Patent Provisional Publication No. 47(1972)-41830 describes that an image is directly transferred onto the permanent support made of an art paper or a coat paper using the above-mentioned method.
However, these methods also have various defects. That is, the final image transferred onto the permanent support is reversed in right and left to the original. Further, in the case of using the heat-fusible polymer as an adhesive, a high temperature for the transference is required because a melting point of the polymer generally is high, and the dimensional stability of the support is reduced by influence of heat, whereby the positions of the transferred images become discrepant from each other. On the contrary, in the case of using a heat-fusible polymer having a low melting point as an adhesive, unfavorable adhesion is brought about after image formation, or the surface of the final image is easily damaged.
As a method of improving the above defects, Japanese Patent Provisional Publication No. 59(1984)-97140 describes a method of temporarily transferring a color image onto a temporary image-receiving sheet (referred to simply as "image-receiving sheet" hereinafter) prior to the transference of the color image onto a permanent support. In this method, an image-receiving sheet having an image-receiving layer made of a photopolymerizable material such as an ethylenic polyfunctional monomer (this image-receiving layer is also referred to as "a photopolymerizable image-receiving layer" or "a photopolymerizable adhesive layer") on a support is prepared. Onto the image-receiving sheet, color images are temporarily transferred one after another to form a laminate of the color images on the photopolymerizable image-receiving layer, before each color image is transferred onto the permanent support. Thereafter, the laminate of the color images is transferred onto the permanent support with the photopolymerizable image-receiving layer, and then the transferred photopolymerizable image-receiving layer is wholly exposed to light on the permanent support to cure the transferred photopolymerizable image-receiving layer.
This image-transferring method using the image-receiving sheet solves the above-mentioned problems and further has an advantage that an erect image of the mask original can be obtained on the permanent support. Moreover, since the photopolymerizable image-receiving layer of the image-receiving sheet contains an ethylenic polyfunctional monomer, the photopolymerizable image-receiving layer itself is soft and transference of images at a low temperature is possible. In addition, after the transference of images, the photopolymerizable image-receiving layer can be easily cured by the exposure to light on the whole surface. Accordingly, any adhesion is not brought about after the images are transferred, and the final image is resistant to damage, so that this image-transferring method is an advantageous image-forming method in practical use.
However, the image-receiving sheet used in the method described in Japanese Patent Provisional Publication No. 59(1984)-97140 still has a problem that the adhesion strength between the photopolymerizable image-receiving layer (i.e., photopolymerizable adhesive layer) and the support is disadvantageously high when the image-receiving layer is in the unexposed state (i.e., unpolymerized state). That is, in the case that the photopolymerizable adhesive layer with the laminate of each color images is transferred onto the final support (permanent support), and then the support of the image-receiving sheet is peeled off prior to the exposure operation, peel lines (streaks) easily occur on the surface of the transferred photopolymerizable adhesive layer. For this reason, the method described in Japanese Patent Provisional Publication No. 59(1984)-97140 adopts a process comprising the steps of transferring the photopolymerizable adhesive layer having images thereon onto the final support, then subjecting the layer to exposure to light on the whole surface to cure the photopolymerizable adhesive layer so as to lower the adhesion strength between the photopolymerizable adhesive layer and the support of the image-receiving sheet, and then removing the support of the image-receiving sheet.
In the method of forming an image by way of transference of an image (i.e., image transferring method), a photosensitive laminate comprising a support, a subbing layer (e.g., a peel layer) made of an organic polymer and a photosensitive image-forming layer superposed in this order is employed as a photosensitive transfer material, as described before. The photosensitive transfer material may be further provided with a barrier layer between the peel layer and the image-forming layer to prevent occurrence of color material fogging on the non-image portion obtained after developing procedure.
In the process for preparing a color proof used for color proofing utilizing a photosensitive transfer material, photosensitive transfer materials for each colors (four colors) are prepared in the first place; then, they are exposed to light and developed to form an image of individual color on the image-forming layer of each photosensitive transfer material; thereafter, the obtained image-formed layers of each colors are transferred with the peel layer onto the image-receiving sheet one after another under application of heat and pressure with adjusting (joining) positions of those color images. Therefore, on the surface of the image-receiving sheet after the transference of the first color image, a peel layer of the first transferred color image is present. When the position of the second color image is tried to be joined with the position of the first color image to transfer the second color image onto the first color image, adjustment (joining) of the image positions is hardly made because the slipperiness between film surfaces of the images to be joined is insufficient owing to tackiness and adhesiveness of the peel layer, resulting in deterioration of workability. Further, there has been found other defect that air is drawn into between film surfaces of the images when ununiform force is applied during the transferring stage, whereby air bubbles are included in the transferred image. The inclusion of air bubbles in the obtained image (the latter defect) causes no problem in practical use, but it is unfavorable from the viewpoint of commercial value.
The above-mentioned problems such as reduction in slipperiness between film surfaces and inclusion of air bubbles are markedly shown between the peel layer previously laminated on the image-receiving sheet and the image layer superposed thereon, for example, between the surface of the non-image portion (peel layer) of the first color image and the surface of the image portion of the second color image. However, the same problems are also shown in a photosensitive transfer material having a barrier layer between the peel layer and the image-forming layer, as far as the barrier layer basically has such characteristics as tackiness and heat-adhesiveness.
For solving the above-mentioned problems, it has been proposed that matting agent particles such as silica particles are introduced into the peel layer, but in the case of using the known matting agent particles, the particles are unstable in a coating solution (i.e., coating solution for the formation of a peel layer), or the adhesive strength in the transferring stage is reduced, and as a result, uniform adhesion is hardly made.